In a court filing obtained by The Associated Press, Nunberg accused Trump of trying to silence him "in a misguided attempt to cover up media coverage of an apparent affair" between two senior campaign staffers.

Such a legal dispute is highly unusual for a presidential candidate. It reflects Trump's efforts to aggressively protect the secrecy of his campaign's inner workings, as he has for years fought to protect the secrecy of his businesses and family.

The AP reported last month that Trump requires nearly everyone in his campaign and businesses to sign legally binding nondisclosure agreements prohibiting them from releasing any confidential or disparaging information about the real estate mogul, his family or his companies. Trump has also said he would consider requiring such agreements in the White House.

Nunberg's filing comes at a crucial political moment for Trump. He's on the verge of picking his running mate and is preparing for next week's Republican convention, one of his highest profile opportunities to reach voters and ease the concerns of GOP leaders who are concerned about his unconventional candidacy.

In the court filings, Nunberg denied disparaging Trump and accused the presumptive GOP nominee of attempting to "bully" him into silence after Nunberg decided to publicly support Texas Sen. Ted Cruz's presidential bid.

"Mr. Trump's actions in starting a $10 million arbitration, seeking to silence Mr. Nunberg and have the proceedings sealed are a cautionary tale of what the American people face if Mr. Trump is elected president," said Andrew Miltenberg, Nunberg's attorney. Miltenberg said Trump's attorney argued for the documents to be sealed in a hearing Wednesday morning.

Trump attorney Alan Garten repeatedly declined to refer to Nunberg by name, but described him as "a person who has a history of making untrue, outlandish and outrageous allegations."

Nunberg was a consultant to Trump's presidential campaign but was fired in August because of racist posts he wrote on Facebook.

Nunberg has been highly critical of Trump's former campaign manager Corey Lewandowski, both professionally and personally. In a recent GQ Magazine interview, he said he would suck the "blood of out of (Lewandowski's) skull by the time I'm done with him."

In the court filings, Nunberg said Trump filed a $10 million arbitration claim against him and falsely accused him of being a source of a New York Post story from mid-May that recounted a public quarrel between Lewandowski and campaign spokeswoman Hope Hicks. Lewandowski was fired from the campaign in June after months of tension with other senior Trump advisers.

Nunberg denied being the source of the article, but in court papers referred to the quarrel as being part of an "apparent affair."

Garten told the AP that Nunberg's allegations about Hicks and Lewandowski are "categorically untrue." Reached by phone, Lewandowski said he was "not familiar with the court case" and would not comment on Nunberg's allegations.

Hicks did not respond to detailed requests to respond to the allegations sent via email and text, as well as a voicemail.

Lewandowski helped Trump upset 16 primary rivals, a stunning feat for the political novice and a campaign manager with little presidential campaign experience. But Lewandowski clashed with other campaign staffers and was viewed by GOP leaders as unprepared to oversee a general election campaign.

Since Lewandowski's firing, Trump's campaign has shown flashes of operating more professionally, with the candidate giving more prepared speeches in addition to his freewheeling rallies.

Nunberg's filed the court documents in an attempt to block private arbitration proceedings initiated by Trump in May.

In addition to asserting a right to discuss the campaign on free speech grounds, Nunberg's lawsuit also argued that the campaign's arbitration claim was invalid because it was brought by an exploratory group Trump formed for his 2012 campaign, "which has nothing to do with the Trump Campaign's activities in the 2016 presidential campaign cycle."

"The Trump Campaign was not in existence prior to or at the time of the agreement, and Mr. Nunberg did not agree or intend that it apply to any future entity such as the Trump Campaign," Nunberg's complaint said.

In an affidavit, Nunberg's mother, Rebecca Citron Nunberg, said the Trump entity bringing the claim against her son is not registered in the state of New York, depriving it of its ability to pursue legal claims against him.

FILE- In this May 23, 2005 file photo, real estate mogul and Reality TV star Donald Trump, left, listens as Michael Sexton introduces him at a news conference in New York where he announced the establishment of Trump University. A federal judge who has been a target of Donald Trump’s unending scorn must decide whether to release videos of the presumed Republican presidential nominee testifying in a lawsuit about the now-defunct Trump University, images that Trump’s attorneys worry will be used to tarnish the campaign. (AP Photo/Bebeto Matthews, File)

FILE - In this May 12, 2016 file photo, Republican presidential candidate Donald Trump's campaign communications manager Hope Hicks, right, and Daniel Scavino Jr., Director for Social Media for Trump Campaign walk to their motorcade vehicle after Trump's visit to Jones Day's D.C. law offices in Washington. The Associated Press reported last month that Trump requires nearly everyone in his campaign and businesses to sign legally binding nondisclosure agreements prohibiting them from releasing any confidential or disparaging information about the real estate mogul, his family or his companies. Trump has also said he would consider requiring such agreements in the White House. (AP Photo/Pablo Martinez Monsivais, File)

FILE - In this April 3, 2016 file photo, Corey Lewandowski talks to a member of the media at Nathan Hale High School in West Allis, Wis. The Associated Press reported last month that Trump requires nearly everyone in his campaign and businesses to sign legally binding nondisclosure agreements prohibiting them from releasing any confidential or disparaging information about the real estate mogul, his family or his companies. Trump has also said he would consider requiring such agreements in the White House. (AP Photo/Charles Rex Arbogast, File)

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